Beam experiment backgrounds can be reduced by splitting the reactor core so that beam ports view moderator rather than fuel. Multigroup calculations have been performed on D2O and H2O split core reactors. Measurements of flux distributions for an H2O split core are in agreement with the calculations. Thermal flux in the center of the moderator gap is greater than a standard core flux at the same power. The fast neutron and gamma ray spectra have been calculated for a beam port viewing moderator and viewing fuel. Measurements of fast neutron current from an H2O reactor using an aluminum threshold detector indicate a factor of 10 reduction in fast flux by viewing moderator. The control characteristics of D2O and H2O split cores do not appear significantly different from those of standard cores.